How concerning is secondary polycythemia?

Underlying cause: It all depends on the underlying cause of your Secondary polycythemia. The most common cause of polycythemia is low oxygen (hypoxia) secondary to lung (pulmonary) disease like emphysema, R to L shunts in heart or some arterio venous malformation in your lung is resent. All these can cause low blood Oxygen level and thus your kidney responds by increasing Erythropoietin which stimulates your bone